This invention relates to a suture (surgical) needle and a method of and apparatus for grinding a needle material to form a suture needle having a cutting edge.
A general method of producing a suture needle having a cutting edge will now be briefly described.
First, a wire is cut into a predetermined length to provide an elongated needle material. Then, a mounting hole to which a gut is to be attached is formed in one end portion of the needle material. Then, the needle material is pressed into a required cross-sectional shape. Then, the needle material is ground to form a cutting edge. Then, the needle material is bent into a required shape. Then, the needle material is subjected to a heat treatment, and then is subjected to chemical polishing and/or electropolishing. Finally, a silicone coating is optionally applied to the needle thus produced.
Japanese Patent Publication No. 35383/88 discloses one method of grinding a needle material. This method will now be described in detail with reference to FIG. 14. In this method, there are used a whetstone 90 with a cylindrical peripheral surface and a chucking jig 91. A needle material 100 having a mounting hole formed in its one end portion is chucked or held by the chucking jig 91, and is pressed against the peripheral surface of the whetstone 90 in such a manner that the needle material 100 is oriented perpendicular to an axis 90a of rotation of the whetstone 90. The needle material 100 is ground by the rotation of the whetstone 90, and as a result a cutting edge is formed at one or each of lateral edges of the ground surface of the needle material, and at the same time the end of the needle material remote from the one end portion thereof chucked by the chucking jig 91 is pointed.
This method has the following disadvantages (1) to (4):
(1) The grinding direction (that is, the direction of movement of abrasive grains bonded to the peripheral surface of the whetstone) is generally parallel to the longitudinal direction of the needle material, and hence is substantially parallel to the cutting edge produced by the grinding. Therefore, burrs formed on the cutting edge are considerably large. When these burrs are to be removed by electropolishing or chemical polishing, it is difficult to determine a proper time for such polishing treatment. More specifically, if the treatment time is too short, the burrs fails to be removed to a satisfactory level, and in contrast if the treatment time is too long, the cutting edge becomes rounded. In either case, the piercing properties of the resultant suture needle are adversely affected.
(2) The direction of rotation of the whetstone 90 during the grinding is so determined that the abrasive grains bonded to the peripheral surface of the whetstone 90 move in a direction away from the chucked end of the needle material 100 toward the pointed end thereof. The reason for this is to prevent the pointed end of the needle material 100 from interfering with the peripheral surface of the whetstone 90. However, with this rotation direction, the heat produced by the grinding concentrates on the pointed end of the needle material 100, having a small heat capacity, to soften the pointed end of the needle material 100, so that the piercing properties and strength of the resultant suture needle are adversely affected.
(3) The condition of the peripheral surface of the whetstone 90 is changed little by little in the course of a long-period use, and as a result the condition of the cutting edge obtained by the grinding is changed little by little from one needle material to another.
(4) As shown in FIG. 14, when the needle material 100 is pressed against the peripheral surface of the whetstone 90, the chucking jig 91 must be held apart from the peripheral surface of the whetstone 90. This does not pose any problem when grinding the needle material for a long suture needle, but poses a problem when grinding the needle material for a short suture needle used for an operation on the eye. When the needle material is short, the chucking jig 91 must be located at a position shown in phantom in FIG. 14; however, at this position, the chucking jig 91 interferes with the whetstone 90. Therefore, actually, the chucking jig 91 is located at the position shown in a solid line in FIG. 14, and the needle material must be much longer than the resultant suture needle. This requires an additional step of cutting the needle material after the grinding step, and after this cutting step, the step of forming the mounting hole in the end of the needle material must be carried out. During the cutting step and the mounting hole-forming step, it is possible that the cutting edges of a number of the needle materials are contacted with one another, and are damaged, which adversely affects the piercing properties of the cutting edges. And besides, because of the additional cutting step and the waste of the material, the manufacturing cost of the suture needle is increased.
In another conventional method of grinding a needle material, there is used an endless abrasive sheet extended around a pair of rollers. This abrasive sheet comprises a sheet-like substrate made of a cloth, paper or the like, and abrasive grains bonded to an outer surface of this substrate. In this method, a chucking jig disposed near the peripheral surface of the roller chucks the needle material in such a manner that the needle material is oriented in parallel relation to the direction of movement of the abrasive sheet, and the needle material is pressed against that portion of the abrasive sheet extended around the peripheral surface of the roller. This method also has the above-mentioned disadvantages (1) to (4).
Japanese Utility Model Publication Nos. 39420/76, 41208/80 and 6885/86 and Japanese Laid-Open (Kokai) Utility Model Application No. 135106/85 disclose suture needles having a number of grinding traces extending perpendicular to a cutting edge. Although a grinding method is not clearly described in these prior art publications, it is clear that abrasive grains move in a direction perpendicular to the cutting edge to effect the grinding. In such method, the above disadvantage (2) is overcome, and probably the above disadvantage (4) may be overcome. However, the above disadvantage (3) is not overcome, and instead of the above disadvantage (1), another disadvantage is encountered. More specifically, large burrs are formed on one of the two cutting edges which is disposed at a downstream side of the direction of movement of the abrasive grains, the two cutting edges being formed respectively on the lateral edges of the ground surface of the needle material. Burrs are hardly formed on the other cutting edge disposed at an upstream side of the direction of movement of the abrasive grains. Therefore, when the burrs on the downstream-side cutting edge are removed by electropolishing or chemical polishing after the grinding operation, the upstream-side cutting edge becomes rounded. This adversely affects the piercing properties of the resultant suture needle.